bevel modifier does not seem to work
Ok, so there seems to be a few things going on here. Firstly, and I don't know if this is intentional, but your single mesh object is comprised of 2 different pieces sitting on top of one another:

As you can see from the image, both of the pieces seem to have some parts that don't belong. I separated the pieces only for this example image, you don't have to do it yourself, unless you want to delete a piece or something. If you need to separate them, select a face and press L. This will select everything that is part of the same &quot;piece&quot;. You can then move it away, or whatever.
You can get rid of the stuff that doesn't belong (pieces separated or not) by pressing M (Merge) and selecting &quot;By Distance&quot;. This removes duplicated or overlapping vertices. Doing this to yours removed 24 vertices - you can see the count in the bottom right corner when you perform the operation.

Lastly the bevel is still a bit off as the result of non-uniform scale (result of scaling in object mode). To fix this, in object mode, select your object, Press Ctrl + A and select &quot;Scale&quot;.